Machine-to-machine (m2m) terminal, base station, method, and computer readable medium

ABSTRACT

A Machine-to-machine (M2M) terminal ( 11 ) is configured to receive a first notification from a base station ( 13 ) and to transmit a second notification to the base station ( 13 ) when establishing a radio connection with the base station ( 13 ) after reception of the first notification or while performing a procedure for establishing a bearer between the M2M terminal ( 11 ) and a core network ( 14 ) after reception of the first notification. The first notification indicates whether specific coverage enhancement processing is supported in a cell ( 130 ) of the base station ( 13 ) in which the M2M terminal ( 11 ) is located. The second notification indicates that the specific coverage enhancement processing is required or being executed by the M2M terminal ( 11 ). It is thus possible to provide an improvement to allow the M2M terminal to determine necessity of special coverage enhancement processing for M2M terminals.

TECHNICAL FIELD

The present disclosure relates to a radio communication system whichperforms a communication control in order to enhance coverage.

TECHNICAL FIELD

In the 3GPP Long Term Evolution (LTE), standardization of techniques forimproving deterioration of communication quality due to recent sharpincrease in mobile traffic and for achieving faster communication hasbeen performed. Further, standardization of techniques for avoidingincrease in a control signaling load due to connections of an enormousnumber of Machine to Machine (M2M) terminals to an LTE network has beenperformed (Non-Patent Literature 1). The M2M terminals are, for example,terminals that perform communication without human intervention. The M2Mterminals are placed in various types of equipment including machines(e.g., vending machines, gas meters, electric meters, vehicles, railwayvehicles, and ships) and sensors (e.g., environmental, agricultural, andtraffic sensors). In the LTE, communication performed by the M2Mterminals are referred to as Machine Type Communications (MTC) and aterminal performing the MTC is referred to as an MTC terminal (MTC UserEquipment (MTC UE)).

While M2M service providers need to distribute an enormous number of M2Mterminals, there is a limit to the cost allowable for each M2M terminal.Therefore, it is required M2M terminals be implemented at a low cost,and M2M terminals be able to perform communication with low powerconsumption, for example. Further, in one use case, MTC UEs performcommunication while they are fixedly or statically installed inbuildings. In this case, the radio quality of MTC UEs may be always lowand accordingly coverage enhancement technique is especially needed forMTC devices compared to normal UEs having mobility (e.g., mobiletelephones, smartphones, tablet computers, and notebook personalcomputers (notebook PCs)). Further, functional restrictions contributingto reduction of the cost include, for example, a low maximumtransmission power, a small number of reception antennas, no support ofhigh-order modulation schemes (e.g., 64 Quadrature Amplitude Modulation(64QAM)), and a narrow operating bandwidth (e.g., 1.25 MHz), which lowerthe maximum transmission rate of MTC UEs. Therefore, in the LTE,standardization of techniques for enhancing communicationcharacteristics of MTC UEs (i.e., coverage), which are expected to belower than those of normal UE has been performed (Non-Patent Literature2). In the following description, some examples of the techniques forenhancing coverage of MTC UEs discussed in the LTE are described. It canbe said that the coverage enhancement techniques (coverage enhancementprocessing) for MTC UEs described below are processing for enhancing orimproving communication characteristics or communication quality of MTCUEs. The state of a UE to which these special coverage enhancementtechniques has been applied is referred to as a coverage enhancementmode (Enhanced Coverage Mode (ECM)).

The ECM can improve, for example, a reception characteristic of aPhysical Broadcast Channel (PBCH), a transmission characteristic of aPhysical Random Access Channel (PRACH) preamble (i.e., detectioncharacteristic in an eNB), a reception characteristic of a PhysicalDownlink Shared Channel (PDSCH), and a transmission characteristic of aPhysical Uplink Shared Channel (PUSCH). The PBCH is a downlink broadcastchannel used by an eNB to transmit broadcast information commonly usedwithin a cell. The PRACH is an uplink physical channel used by a UE foran initial access to a radio base station (eNB). The PDSCH is a downlinkphysical channel used for data reception by a UE. The PUSCH is an uplinkphysical channel used for data transmission by a UE.

One processing that is being discussed to improve a receptioncharacteristic of the PBCH is to repeatedly transmit broadcastinformation on the PBCH a number of extra times as compared to thenormal operation by a predetermined number of times (Non-PatentLiterature 3). One processing that is being discussed to improve atransmission characteristic of the PRACH is to repeatedly transmit thePRACH (i.e., preamble) a predetermined number of times (Non-PatentLiterature 4). Further, one processing that is being discussed toimprove a reception characteristic of the PDSCH and a transmissioncharacteristic of the PUSCH is to repeatedly transmit the PDSCH and thePUSCH over multiple subframes (Non-Patent Literature 5). According tothe above processing, communication characteristics of MTC UEs that isexpected to be lower than that of normal UEs will be improved.

It is expected that the coverage enhancement processing in the ECM isperformed for MTC UEs that perform a delay tolerant access. The delaytolerant access is defined as being a new EstablishmentCause that isspecified in an RRC Connection Request message and is used, for example,to control an overload. The delay tolerant access is mainly intended forMTC UEs that execute a delay-tolerant MTC application. For example, in ametering service (meter reading service), there is no need to send ametering report to a remote system in real time (or in exactcommunication cycles) and a long delay may be allowed for thetransmission of the metering report. When an eNB imposes overloadcontrol on the delay tolerant access, the eNB may reject an RRCConnection Request transmitted by a RRC Connection Request message thatcontains “EstablishmentCause” indicating the delay tolerant access.

CITATION LIST Non Patent Literature

-   [Non-Patent Literature 1] 3GPP TR 37.868 V11.0.0 (2011-09), “3rd    Generation Partnership Project; Technical Specification Group Radio    Access Network; Study on RAN Improvements for Machine-type    Communications; (Release 11)”, September, 2011-   [Non-Patent Literature 2] 3GPP TR 36.888 V12.0.0 (2013-06), “3rd    Generation Partnership Project; Technical Specification Group Radio    Access Network; Study on provision of low-cost Machine-Type    Communications (MTC) User Equipments (UEs) based on LTE (Release    12)”, June, 2013-   [Non-Patent Literature 3] 3GPP R1-135943, Vodafone, “Way Forward on    P-BCH for MTC enhanced coverage”, 3GPP TSG RAN WG1 #75, San    Francisco, USA, 11-15 Nov. 2013-   [Non-Patent Literature 4] 3GPP R1-135944, Vodafone, “Way Forward on    PRACH for MTC enhanced coverage”, 3GPP TSG RAN WG1 #75, San    Francisco, USA, 11-15 Nov. 2013-   [Non-Patent Literature 5] 3GPP R1-136001, Vodafone et al. “Way    forward on PDCCH, PDSCH, PUCCH and PUSCH for MTC enhanced coverage”,    3GPP TSG RAN WG1 #75, San Francisco, USA, 11-15 Nov. 2013

SUMMARY OF INVENTION Technical Problem

The present inventor has examined many problems that are caused when thecoverage enhancement processing in the ECM is applied to MTC UEs (M2Mterminals). For example, while PBCH repetition is commonly applied toMTC UEs in a cell, RACH repetition and PDSCH/PUSCH repetition areseparately applied to each MTC UE.

In one example, an eNB may determine whether the ECM, in particular,coverage enhancement processing on a per-MTC-UE basis (e.g., RACHrepetition and PDSCH/PUSCH repetition) is required for a specific MTC UEor not. Since PDSCH/PUSCH repetition requires allocation of radioresources by an eNB, it may be reasonable that the necessity of thecoverage enhancement processing on a per-MTC-UE basis is determined bythe eNB.

On the other hand, however, that the necessity of the ECM is determinedby an eNB may cause problems. For example, If an MTC UE cannot start theECM until an eNB has determined the necessity of the ECM (in particular,the coverage enhancement processing on a per-MTC-UE basis) for thisspecific MTC UE, the MTC UE cannot benefit from the improvement ofcommunication characteristics by the ECM until the determination in theeNB has been completed. This may cause increase in delay time until theMTC UE becomes able to benefit from the improvement of communicationcharacteristics by the ECM. Accordingly, in the worst case, the MTC UEmay fail the first access to the eNB (e.g., random access on the PRACH,or procedure for establishing a radio connection (Radio Resource Control(RRC) Connection)).

In view of the above, one exemplary object of embodiments disclosed inthe specification is to provide an MTC UE (M2M terminal), a basestation, a method, and a program that are improved to allow the MTC UEto determine necessity of special coverage enhancement processing forMTC UEs (e.g., coverage enhancement processing in the ECM). It should benoted that this object is merely one of objects accomplished by theembodiments disclosed in the specification. The other objects orproblems and novel features will be made apparent from the specificationor the accompanying drawings.

Solution to Problem

In one aspect, an M2M terminal includes a radio communication unit and acontroller. The radio communication unit is configured to communicatewith a base station. The controller is configured to receive a firstnotification from the base station, and to transmit a secondnotification to the base station when establishing a radio connectionwith the base station after reception of the first notification or whileperforming a procedure for establishing a bearer between the M2Mterminal and a core network after reception of the first notification.The first notification indicates whether specific coverage enhancementprocessing is supported in a cell of the base station in which the M2Mterminal is located. The second notification indicates that the specificcoverage enhancement processing is required or being executed by the M2Mterminal.

In one aspect, a base station includes a radio communication unit and acontroller. The radio communication unit is configured to communicatewith an M2M terminal. The controller is configured to transmit, via theradio communication unit, a first notification indicating that specificcoverage enhancement processing for the M2M terminal is supported in acell of the base station in which the M2M terminal is located.

In one aspect, a method performed by an M2M terminal includes (a)receiving a first notification from a base station, and (b) transmittinga second notification to the base station when establishing a radioconnection with the base station after reception of the firstnotification or while performing a procedure for establishing a bearerbetween the M2M terminal and a core network after reception of the firstnotification. The first notification indicates whether specific coverageenhancement processing is supported in a cell of the base station inwhich the M2M terminal is located. The second notification indicatesthat the specific coverage enhancement processing is required or beingexecuted by the M2M terminal.

In one aspect, a method performed by a base station includestransmitting a first notification in a cell of the base station in whichan M2M terminal is located. The first notification indicates thatspecific coverage enhancement processing for the M2M terminal issupported in the cell.

In one aspect, a program contains a set of instructions (software codes)which, when loaded into a computer, causes the computer to perform anyone of the aforementioned methods.

Advantageous Effects of Invention

According to the above aspects, it is possible to provide an MTC UE (M2Mterminal), a base station, a method, and a program that are improved toallow the MTC UE to determine necessity of special coverage enhancementprocessing for MTC UEs. It should be noted that this effect is merelyone of effects expected to be brought about by the embodiments disclosedin the specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a configuration example of a radiocommunication system according to a first embodiment;

FIG. 2 is a sequence diagram showing one example of communicationprocedures according to the first embodiment;

FIG. 3 is a sequence diagram showing another example of thecommunication procedures according to the first embodiment;

FIG. 4 is a sequence diagram showing one example of communicationprocedures according to a second embodiment;

FIG. 5 is a sequence diagram showing one example of communicationprocedures according to a third embodiment;

FIG. 6 is a sequence diagram showing one example of communicationprocedures according to a fourth embodiment;

FIG. 7 is a block diagram showing a configuration example of an M2Mterminal (MTC UE) according to embodiments of the present invention; and

FIG. 8 is a block diagram showing a configuration example of a basestation (eNB) according to embodiments of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, specific embodiments will be described in detail withreference to the drawings. The same or corresponding components aredenoted by the same reference symbols throughout the drawings, andrepetitive explanations will be omitted as necessary for the sake ofclarity.

Each of embodiments described below may be implemented independently orin combination with any other. These embodiments include novelcharacteristics different from one another. Accordingly, theseembodiments contribute to achieving objects or solving problemsdifferent from one another and contribute to obtaining advantagesdifferent from one another.

First Embodiment

FIG. 1 shows a configuration example of a radio communication systemaccording to this embodiment. This radio communication system providescommunication services, such as voice communication or packet datacommunication or both, for example. With reference to FIG. 1, the radiocommunication system includes M2M terminals 11 (11A, 11B, 11C), a normalradio terminal 12 which is not an M2M terminal, a base station 13, and acore network 14. The radio terminal 12 is, for example, a mobiletelephone, a smartphone, a tablet computer, or a notebook PC. The M2Mterminals 11A, 11B, and 11C, and the radio terminal 12 are located in acell 130 of the base station 13. In this embodiment, the radiocommunication system is described as being a 3GPP LTE system. That is,the M2M terminals 11 correspond to MTC UEs, the radio terminal 12corresponds to a normal UE which is not an MTC UE, the base station 13corresponds to an eNodeB (eNB), and the core network 14 corresponds toan Evolved Packet Core (EPC).

In FIG. 1, the distance between the MTC UE 11A and the eNB 13 is largerthan the distance between the MTC UE 11B and the eNB 13. Accordingly, itis assumed that the MTC UE 11A has a large pathloss and its radioquality is degraded. Further, the MTC UE 11C is installed in a buildingand, accordingly, it is thus assumed that its radio quality is moredegraded compared to a case in which the MTC UE 11C is located outdoors.Furthermore, if the capabilities or functions of the MTC UEs 11 (11A,11B, and 11C) are limited compared to those of the normal UE 12 (e.g., alower maximum transmission power, a smaller number of receptionantennas, no support of high-order modulations), it is expected thatdegradation in radio quality of the MTC UEs 11 will become more serious.Therefore, the MTC UEs 11 according to this embodiment are configured tosupport the aforementioned Enhanced Coverage Mode (ECM) and to performcoverage enhancement processing in the ECM.

As already stated above, the coverage enhancement processing in the ECMcan be said as processing for enhancing or improving communicationcharacteristics (communication quality) of MTC UEs. As already statedabove, the coverage enhancement processing in the ECM may include atleast one of the following processing (a) to (d) or may include otherprocessing (e.g., (e) and (f)):

(a) Repeatedly transmitting broadcast information on a PBCH a number ofextra times as compared to the normal operation by a predeterminednumber of times;(b) Repeatedly transmitting a PPACH (PRACH preamble) a predeterminednumber of times;(c) Repeatedly transmitting a PDSCH over multiple subframes;(d) Repeatedly transmitting a PUSCH over multiple subframes;(e) Increasing the power spectral density (PSD) of one or both of aPDSCH and a PUSCH (PSD boosting); and(f) Performing frequency hopping during repetitive transmission of oneor both of a PDSCH and a PUSCH.

The subframe is a unit constituting a LTE radio frame. One radio framehas a length of ten milliseconds and is composed of ten subframes.Therefore, one subframe has a length of one millisecond. One subframeincludes 14 symbols in a time domain (single carrier frequency divisionmultiple access (SC-FDMA) symbols in uplink and orthogonal frequencydivision multiplexing (OFDM) symbols in downlink).

In the following description, communication control for the ECMaccording to this embodiment is described. The eNB 13 according to thisembodiment transmits, in the cell 130, a first notification indicatingthat specific coverage enhancement processing for MTC UEs (M2Mterminals) (i.e., the coverage enhancement processing in the ECM) issupported in the cell 130 of the eNB 13. The first notification mayindicate whether the ECM is supported, on a per-base-station basis(i.e., supported in all the cells of the eNB 13) or on a per-cell basis.The MTC UE 11 receives the first notification from the eNB 13. The MTCUE 11 then transmits a second notification to the eNB 13 after receptionof the first notification. The MTC UE 11 may transmit the secondnotification in response to receiving the first notification from theeNB 13. The MTC UE 11 transmits the second notification to the eNB 13when establishing a radio connection (RRC Connection) with the eNB 13 orwhile performing a procedure for establishing a bearer between the MTCUE 11 and the EPC 14 (i.e., Evolved Packet System (EPS) bearer). Thesecond notification indicates that the coverage enhancement processingin the ECM is required by the MTC UE 11 or is being executed by the MTCUE 11.

According to this embodiment, the following effects can be expected.That is, if the MTC UE 11 cannot start the ECM until the eNB 13 hasdetermined the necessity of the ECM for the MTC UE 11 (in particular,the coverage enhancement processing dedicated for the specific MTC UE11), the MTC UE 11 cannot benefit from the improvement of communicationcharacteristics by the ECM until the determination in the eNB 13 hasbeen completed. This may cause increase in delay time until the MTC UE11 becomes able to benefit from the enhancement of communicationcharacteristics by the ECM. Accordingly, in the worst case, the MTC UE11 fails the first access to the eNB 13 (e.g., random access on thePRACH, or procedure for establishing a radio connection (RRCConnection)).

In order to deal with these problems, the eNB 13 according to thisembodiment transmits the aforementioned first notification in the cell130. Accordingly, the MTC UE 11 according to this embodiment can knowthat the ECM is supported in the cell 130 of the eNB 13 and can transmitthe second notification, which indicates the coverage enhancementprocessing in the ECM is required or being executed by the MTC UE 11, tothe eNB 13 when establishing a radio connection (RRC Connection) orwhile performing an EPS bearer establishment procedure. In most cases,UEs including the MTC UEs 11 measure the radio quality in an idle statebefore transitioning from an idle state (RRC_IDLE) to a connected state(RRC_CONNECTED) at a periodic or non-periodic communication opportunity.Accordingly, the MTC UE 11 may receive the first notification from theeNB during the idle state and determine the necessity of the ECM basedon the radio quality, which is measured during the idle state, prior toarrival of a communication opportunity. It is therefore possible tocontribute to a reduction in delay time (delay time until the ECM isstarted) due to waiting for determination by the eNB 13 of necessity ofthe ECM after arrival of the communication opportunity.

The terms “idle state” and “connected state” used in the specificationis defined as follows. The “idle state” is a state in which a radioconnection between a UE and an eNB has been released. Accordingly, theeNB has no information (UE context) regarding the UE in the idle state.The location of the UE in the idle state is tracked by a core network atlocation-registration-area level (e.g., tracking area or routing area).The core network can reach the UE in the idle state by paging. Further,the UE in the idle state cannot perform unicast data transmission to orfrom the eNB. Accordingly, the UE in the idle state should transition tothe connected state in order to perform unicast data transmission.Examples of the idle state include: (1) an RRC idle state in a UniversalTerrestrial Radio Access Network (UTRAN); (2) an RRC_IDLE state in anEvolved UTRAN (E-UTRAN); and (3) an Idle state in WiMAX (IEEE802.16-2004), mobile WiMAX (IEEE 802.16e-2005), and WiMAX2 (IEEE802.16m).

On the other hand, the connected state is a state in which the UE isconnected to the eNB. Accordingly, the eNB has information (UE context)regarding the UE in the connected state. The location of the UE in theconnected state is tracked by the core network at cell level orbase-station level. In most cases, the UE in the connected state canperform unicast data transmission to and from the eNB. However, when theUE is in a CELL_PCH state and a URA_PCH state in the UTRAN, the UEcontext is held by a base station (NodeB), but no dedicated channel isallocated to the UE either in uplink or in downlink. Examples of theconnected state include: (1) an RRC connected state in the UTRAN; (2) anRRC_CONNECTED state in the E-UTRAN; and (3) a connected state in theWiMAX, the mobile WiMAX, and the WiMAX2. Note that, the RRC connectedstate in the UTRAN includes a CELL_DCH state, a CELL_FACH state, aCELL_PCH state, and a URA_PCH state.

Next, specific examples of a method of transmitting the firstnotification from the eNB 13 to the MTC UE 11 and a method oftransmitting the second notification to the eNB 13 from the MTC UE 11are described.

It is preferable that the first notification is transmitted on abroadcast channel that can be received by the MTC UEs 11 having no radioconnection (RRC connection) with the eNB 13, i.e., the MTC UEs 11 in theidle state. In other words, preferably, the first notification isbroadcast information that can be received by the MTC UEs 11 in the idlestate. Specifically, a Broadcast Control Channel (BCCH), which is one ofthe logic channels in the LTE, may be used for transmitting the firstnotification.

More specifically, the first notification is preferably transmitted on abroadcast channel that can be received by each MTC UE 11 that is in theidle state (RCC_IDLE) and further in a detach state (EMM-DEREGISTERED).The detach state (EMM-DEREGISTERED) is one of EPS Mobility Management(EMM) states in the LTE. That is, the detach state (EMM-DEREGISTERED) isa state in which the UE is not registered in a mobility managementelement (e.g., Mobility Management Entity (MME)) in the core network(e.g., EPC) and the mobility management of the UE is not performed. Thelocation information of the UE in the detach state is not tracked by theMME, and, accordingly, the UE in the detach state is unreachable fromthe core network (EPC) by paging. The UE in the detach state needs toperform an initial cell selection (i.e., initial cell research),establish a radio connection with the eNB, and perform locationregistration in the core network (EPC), prior to performingcommunication. The BCCH can also be received by each MTC UE 11 that isin the idle state (RCC_IDLE) and further in the detach state(EMM-DEREGISTERED).

The BCCH is mapped to a transport channel, i.e., a Broadcast Channel(BCH) or a Downlink Shared Channel (DL-SCH). Further, the BCH, which theBCCH has been mapped to, is transmitted by the eNB 13 using a physicalchannel, i.e., a Physical Broadcast Channel (PBCH). The PBCH istransmitted using a predetermined resource block of the first subframein each radio frame and is updated at a period of 40 milliseconds (at aperiod of four radio frames). The broadcast information transmitted onthe PBCH is a Master Information Block (MIB). Therefore, the firstnotification may be contained in the MIB.

On the other hand, the DL-SCH, which the BCCH has been mapped to, istransmitted by the eNB 13 using a physical channel, i.e., a PhysicalDownlink Shared Channel (PDSCH). Although the PDSCH is mainly used totransmit user data, transmission of the BCCH (i.e., broadcastinformation) is specified as one of the special uses of the PDSCH. Theresource block used for the BCCH (broadcast information) is indicated bya control message in a Physical Downlink Control Channel (PDCCH). Thebroadcast information transmitted on the PDSCH is System InformationBlocks (SIBs). Therefore, the first notification may be contained in oneof the existing SIBs (e.g., System Information Block Type 1 (SIB1)).Alternatively, the first notification may be contained in an SIB that isnewly defined for the M2M, MTC UEs, or ECM.

The first notification may indicate whether the ECM is supported in thecell 130 of the eNB 13 either explicitly (e.g., flag bit) or implicitly.The first notification may indicate whether the ECM is supported, on aper-base-station basis (i.e., supported in all the cells of the eNB 13)or on a per-cell basis. The implicit first notification may includeconfiguration information for the coverage enhancement processing in theECM (ECM radio resource configuration or ECM configuration).

The ECM radio resource configuration or ECM configuration may include,for example, at least one of the following information items:

-   -   Configuration information regarding reception of broadcast        information (PBCH);    -   Configuration information regarding reception of system        information (System Information Block (SIB));    -   Configuration information regarding reception of paging (Paging        Channel (PCH));    -   Configuration information regarding reception of downlink        control information (Physical Downlink Control Channel (PDCCH));    -   Configuration information regarding reception of downlink data        (PDSCH);    -   Configuration information regarding transmission of uplink        control information (Physical Uplink Control Channel (PUCCH));    -   Configuration information regarding transmission of uplink data        (PUSCH); and    -   Configuration information regarding measurement reporting of        radio quality (Measurement Report).

The configuration information regarding reception of the broadcastinformation (PBCH) and the configuration information regarding receptionof the system information (SIB) may be, for example, informationindicating which subframe(s) and/or which OFDM symbol(s) is used torepeatedly transmit the broadcast information and (which kind of) systeminformation. The configuration information regarding reception of pagingmay be, for example, information indicating which subframe(s) is used torepeatedly transmit paging. The configuration information regardingreception of the downlink control information (PDCCH) and reception ofthe downlink data (PDSCH) may be, for example, information indicatinghow many times they are repeatedly transmitted or may be informationindicating which subframe(s) is used for repeatedly transmitting them.The configuration information regarding transmission of the uplinkcontrol information (PUCCH) and the transmission of the uplink data(PUSCH) may be, for example, information indicating how many times theyare repeatedly transmitted or may be information indicating whichsubframe(s) is used for repeatedly transmitting them. The configurationinformation regarding measurement reporting of radio quality may be anoffset value or a threshold applied to the measurement result of theradio quality while the ECM is being executed or may be an offset valueor a threshold applied to determination on the report of the measurementresult of the radio quality while the ECM is being executed.

Next, the second notification is described in detail. The secondnotification may be transmitted using, for example, a message forrequesting establishment of a radio connection (RRC connection), i.e.,an RRC Connection Request message. Since an RRC Connection Requestmessage is transmitted first in the RRC connection establishmentprocedure, it can also be said that the second notification istransmitted during a procedure for establishing a radio connection (RRCconnection). From another point of view, the RRC Connection Requestmessage is transmitted in a third step of a random access procedure(Random Access Channel (RACH) procedure). Accordingly, if the RRCConnection Request message is used, it can also be said that the secondnotification is transmitted during a random access procedure (RACHprocedure).

In another example, the second notification may be transmitted using acompletion message indicating completion of establishment of the radioconnection (RRC connection), i.e., an RRC Connection Setup Completemessage. Since the RRC Connection Setup Complete message is the finalmessage transmitted during an RRC connection establishment procedure, itcan be said that the second notification is transmitted during aprocedure for establishing a radio connection (RRC connection). Further,the RRC Connection Setup Complete message contains a NAS message (e.g.,NAS: Service Request, NAS: Attach Request). The RRC Connection SetupComplete message containing a NAS message is the first messagetransmitted during a procedure for establishing an EPS bearer.Therefore, if the RRC Connection Setup Complete message is used, it canbe said that the second notification is transmitted during a bearerestablishment procedure.

By using the RRC Connection Request message or the RRC Connection SetupComplete message for transmitting the second notification, the MTC UE 11can promptly inform the eNB 13 that the MTC UE 11 requires the ECM or isexecuting the ECM, during a procedure for establishing a radioconnection. Thus, for example, the eNB 13 can include the ECMconfiguration in the configuration of the radio connection to beestablished for the MTC UE 11 and can promptly start communication withthe MTC UE 11 using the coverage enhancement processing in the ECM. Itis needless to say that, from the viewpoint of establishment of theradio connection (RRC connection), the second notification may betransmitted using an RRC Connection Reestablishment Complete message,which is similar to the RRC Connection Setup Complete message.

In another example, the second notification may be transmitted during arandom access procedure (RACH procedure) performed prior toestablishment of the radio connection (RRC connection). Specifically,PRACH preamble transmission in the first step of the random accessprocedure (RACH procedure) may be used for transmitting the secondnotification. In this case, the second notification may implicitlyindicate that the ECM is required or being executed by the MTC UE 11 bythe MTC UE 11 using a specific radio resource (e.g., time, frequency,code, or preamble sequence) allocated for the ECM among a plurality ofradio resources for the PRACH.

Since only a PRACH preamble can be transmitted on the PRACH, it may bedifficult to indicate the details of the ECM required or being executedby the MTC UE 11 (e.g., which one or more of coverage enhancementprocesses are specifically required). Therefore, the aforementioned RRCConnection Request message or RRC Connection Setup Complete message maybe more suitable for transmission of the second notification. However,by using the PRACH preamble for transmitting the second notification, itis possible to notify the eNB 13 of the information, which indicateswhether the ECM is required or being executed by the MTC UE 11, muchfaster compared to using the RRC Connection Request message or RRCConnection Setup Complete message.

In the following description, specific examples of processing fordetermining whether the ECM is required by the MTC UE 11 are described.In response to detecting that the ECM is supported in the cell 130 ofthe eNB 13 based on the first notification from the eNB 13, the MTC UE11 may determine whether the ECM (that is, the coverage enhancementprocessing in the ECM) is required in the MTC UE 11.

When the MTC UE 11 determines that the ECM is required, the MTC UE 11may start one or more executable processes selected from a plurality ofcoverage enhancement processes in the ECM. The MTC UE 11 may start, forexample, reception of a PBCH that is repeatedly transmitted, or repeatedtransmission of a PRACH preamble in a random access procedure, or bothof them. Accordingly, the second notification may indicate that the ECMis being executed by the MTC UE 11.

On the other hand, for example, PDSCH/PUSCH repetition requiresallocation of radio resources by the eNB 13. Therefore, the MTC UE 11may notify the eNB 13 of necessity of the coverage enhancementprocessing that the eNB 13 is required to deal with (e.g., PDSCH/PUSCHrepetition). Further, the MTC UE 11 may notify the eNB 13 of necessityof all the coverage enhancement processes in the ECM includingprocessing that can be independently executed in the MTC UE 11 (e.g.,reception of a repeated PBCH, repeated transmission of a PRACHpreamble). Accordingly, the second notification may indicate that theECM is required by the MTC UE 11.

The MTC UE 11 may determine necessity of the ECM (the coverageenhancement processing in the ECM) by considering at least one of accesscause, terminal capability (UE capability), terminal information (UEinformation), communication characteristics (communication performance),and radio quality of the MTC UE 11.

Specific examples of the access cause, terminal capability, terminalinformation, communication characteristics, and radio quality aredescribed below. However, the contents of the access cause, terminalcapability, terminal information, communication characteristics, andradio quality are not limited to them.

The access cause may include at least one of the following two items:

-   -   Purpose of establishing an RRC connection (Establishment cause);        and    -   Service type.

The purpose of establishing an RRC connection may specify, for example,(a) an emergency call (emergency), (b) a high priority access(highPriorityAccess), (c) an access for mobile terminated communication(mt-Access), mobile originated signaling (mo-Signalling), (d) terminaloriginated data transmission (mo-Data), (e) a delay tolerant access(delayTolerantAccess), (f) a low priority access (lowPriorityAccess),(g) an access for small data communication (smallDataAccess), (h) anaccess for small packet communication (smallPacketAccess), (i) a limitedaccess (limitedAccess), (j) an access for a limited service(limitedService), (k) an M2M-type access (m2mAccess), or (l) an accessusing the ECM (ecmAccess).

The service type may specify, for example, (a) a real-time service, (b)a non real-time service, or (c) M2M-type communication.

The terminal capability may include, for example, at least one of thefollowing three items:

-   -   Radio access capability;    -   Device capability; and    -   Terminal category (UE category).

The radio access capability may include, for example, (a) informationindicating whether the UE is supporting the terminal function defined inthe 3GPP LTE (e.g., flag bit) or (b) information indicating whether theUE is supporting the ECM. In order to indicate whether the UE issupporting the ECM, an information element (IE) named “EcmSupport” maybe defined. For example, the true value of “EcmSupport” indicates thatthe ECM is supported (Supported) and the false value thereof indicatesthat the ECM is not supported (NotSupported). Further, an IE named“EnhancedCoverageMode” may be defined. For example, when EcmSupport isset to a value “Supported”, it indicates that the UE is supporting theECM. On the other hand, if the UE does not support the ECM, EcmSupportmay be set to a value “NotSupported”. Alternatively, no sending of thisIE may imply that the UE is not supporting the ECM.

The device capability may include, for example, (a) informationindicating that the UE is an MTC UE, (b) information indicating thatcommunication capability of the UE is limited (compared to that of anormal UE), or (c) information indicating that the UE performs only aspecific communication (e.g., M2M-type communication).

The terminal category may include, for example, (a) informationindicating one of terminal categories defined in the 3GPP LTE or (b)information indicating one of access classes defined in the 3GPP LTE.New terminal category or new access class may be defined for MTC UEsperforming M2M-type communication. For example, a new category (e.g.,category 0) for MTC UEs whose functions are limited in order toimplement it at a low cost may be defined. Further or alternatively, anew access class (AC) that indicates infrequent communication or allowsonly infrequent communication may be defined.

The terminal information may include at least one of the following threeitems:

-   -   Terminal type (UE type);    -   Device type; and    -   Terminal context (UE context).

The terminal type may include, for example, (a) information indicatingwhether the UE is a normal UE (non-MTC UE) or an MTC UE, (b) informationindicating whether the UE has mobility (or information indicating thatthe UE has no mobility), or (c) information indicating whether there isa power supply for the UE.

The device type may include, for example, (a) information indicating thetype of the operating system (OS) installed in the UE or (b) informationindicating the type of the M2M-type communication performed by the UE(i.e., sub-category information of the M2M).

The terminal context may include, for example, (a) information on theaforementioned terminal capability, (b) RRC control informationconfigured in the UE (e.g., information contained in aRadioResourceConfigCommon IE and a RadioResourceConfigDedicated IE), (c)information regarding the mobility of the UE (mobility information), (d)information indicating whether the UE is executing the ECM (ECMexecution information), or (e) information indicating whether the UE hasexecuted the ECM before (e.g., when the UE was in the RRC_CONNECTEDstate last time) (ECM status information).

The communication characteristic may include, for example, at least oneof the following two items:

-   -   Performance measurement result (e.g., L2 measurement); and    -   tatistical communication quality (e.g., KPI).

The performance measurement result may include, for example, (a)measurement results of a block error rate (Block Error Rate), (b)measurement results of a packet error rate (Packet Error Rate), (c)measurement results of throughput (e.g., Scheduled IP Throughput), (d) ameasurement results of packet loss (Packet Loss Rate), or (e)measurement results of packet discard (Packet Discard Rate).

The statistical communication quality may include, for example, (a) thenumber of handover attempts or a handover attempt rate, (b) a handoversuccess rate or a handover failure rate, (c) a communication interval ora communication frequency, (d) a packet occurrence interval or a packetoccurrence frequency, (e) a packet arrival interval (packetinter-arrival time) or a packet arrival frequency (packet inter-arrivalrate), (f) an access interval or an access frequency, or (g) an intervalor a frequency of an RRC connection establishment or a NAS connectionestablishment.

The radio quality may include, for example, at least one of thefollowing two items:

-   -   Received quality of a reference signal (Reference Signal (RS)        received quality); and    -   Channel quality indicator (CQI).

The received quality of a reference signal (RS) may include, forexample, received power (RSRP), (b) reception quality (RSRQ), orreceived power intensity (RSSI) of a downlink RS at the UE.

Determination by the MTC UE 11 of necessity of the ECM can be performedat appropriate times. For example, the MTC UE 11 may determine necessityof the ECM when the MTC UE 11 is powered on, when the MTC UE 11 isperforming initial cell selection (i.e., initial cell research) in theidle state (RRC_IDLE), or when the MTC UE 11 is performing cellreselection in the idle state (RRC_IDLE). By determining necessity ofthe ECM in advance while the MTC UE 11 is in the idle state, it ispossible to contribute to reduction in delay time (delay time until theECM is started) due to waiting for determination by the eNB 13 ofnecessity of the ECM after arrival of the communication opportunity.

Alternatively, the MTC UE 11 may determine necessity of the ECM prior toan access to the eNB 13 to establish a radio connection, at a periodicor non-periodic communication opportunity (e.g., periodic communicationpermitted period, occurrence of non-periodic uplink transmission data,or reception of paging). Alternatively, the MTC UE 11 may determinenecessity of the ECM while the MTC UE 11 is accessing the eNB 13 toestablish a radio connection (e.g., during a RACH access procedure or anRRC Connection establishment procedure). In one more alternative, theMTC UE 11 may determine necessity of the ECM after establishment of aradio connection (RRC connection).

Further, different operations regarding the ECM (i.e., control ofreception or transmission of the MTC UE 11 or eNB 13) may be defined formultiple ECM levels. In this case, the MTC UE 11 may determine not onlywhether the ECM is required (or whether to execute the ECM) but alsowhich operation level is necessary (or which operation level should beexecuted) and send to the eNB 13 the second notification indicating thedetermined level. The eNB 13 may allow for the ECM operation levelreported from the MTC UE 11 based on the second notification sent fromthe MTC UE 11. Alternatively, the eNB 13 may determine a level differentfrom that reported from the MTC UE 11 and send a notification indicatingthe determined level to the MTC UE 11. That is, the eNB 13 may have theauthority to make a final decision on the ECM operation level that theMTC UE 11 should follow.

Further, when the MTC UE 11 determines to execute the ECM or the eNB 13determines to apply the ECM to the MTC UE 11, the MTC UE 11 may continueexecuting the ECM even after transitioning to RRC_IDLE fromRRC_CONNECTED. Further, when the MTC UE 11 determines to execute the ECMor the eNB 13 determines to apply the ECM to the MTC UE 11, the MTC UE11 may continue executing the ECM during a delay tolerant access.

Further, after initial determination of whether the ECM is required (orwhether to execute the ECM), the MTC UE 11 may determine whether tocontinue executing the ECM based on communication characteristics orradio quality of the MTC UE 11. For example, the MTC UE 11 may acquireone or both of a block error rate and a packet error rate as thecommunication characteristics of the MTC UE 11 and may suspend (or stop)the ECM when it determines that one or both of the block error rate andthe packet error rate below a predetermined threshold. Further oralternatively, the MTC UE 11 may acquire one or both of RSRP and RSRQ asthe radio quality and may suspend (or stop) the ECM when it determinesthat one or both of the RSRP and the RSRQ exceed a predeterminedthreshold.

FIG. 2 is a sequence diagram showing one example of operations of theMTC UE 11 and the eNB 13 according to this embodiment. FIG. 2 shows onlythe messages that are necessary for explanation of this embodiment andsome messages included in the procedure specified in the LTE standardare not shown.

In Step S101 of FIG. 2, the eNB 13 broadcasts, in the cell 130, thefirst notification indicating that the eNB 13 is supporting the ECM(System Information Block Type 1x). The first notification may becontained in any one of SIBs, as shown in FIG. 2. As already statedabove, the first notification may indicate whether the eNB 13 (or thecell 130 of the eNB 13) is supporting the ECM either explicitly (e.g.,flag bit) or implicitly. The implicit first notification may includeconfiguration information of radio resources used in the ECM (ECM radioresource configuration).

In Step S102, the MTC UE 11 determines whether the ECM is required (orwhether to execute the ECM) (ECM decision). As already stated above, theMTC UE 11 may perform the determination in Step S102 at a periodic ornon-periodic communication opportunity (e.g., periodic communicationpermitted period, occurrence of non-periodic uplink transmission data,or reception of paging). Alternatively, the MTC UE 11 may perform thedetermination in Step S102 when the MTC UE 11 is powered on, when theMTC UE 11 is performing initial cell selection (i.e., initial cellresearch) in the idle state (RRC_IDLE), or when the MTC UE 11 isperforming cell reselection in the idle state (RRC_IDLE).

As already stated above, the determination in Step S102 may be performedbased on various parameters. For example, this determination may beperformed based on whether the ECM is supported in the cell 130 in whichthe MTC UE 11 is located (or whether the ECM is supported by the eNB 13that manages the cell). This determination may be performed based onwhether the terminal capability (or the device capability) of the MTC UE11 supports the ECM. This determination may be performed based onwhether access cause to the eNB 13 is a delay tolerant access. Thisdetermination may be performed based on whether radio quality of the MTCUE 11 is lower than a predetermined threshold.

FIG. 2 shows a case in which the MTC UE 11 requires the ECM. Therefore,in Step S103, the MTC UE 11 starts executing the ECM (ECM start). InSteps S104 to S108, the MTC UE 11 accesses the eNB 13 while performingthe ECM operations (coverage enhancement processing).

Specifically, in Step S104, the MTC UE 11 transmits a random accesspreamble (PRACH Preamble). In the example shown in FIG. 2, ECM-specificradio resources (e.g., time, frequency, code, preamble sequence) areallocated or available for transmitting the PRACH preamble. Accordingly,the MTC UE 11 transmits a PRACH preamble using any one of theECM-specific radio resources.

In Step S105, the eNB 13 transmits a random access response in responseto detection of the PRACH preamble (Random Access Response). When thePRACH preamble is received on any one of the ECM-specific radioresources, the eNB 13 recognizes that the UE that has transmitted thepreamble is executing the ECM. Accordingly, the radio resources used totransmit the random access response or the transmission mode of therandom access response (e.g., repeated transmission of a PDCCH or PDSCH)may be an ECM-specific one. However, the eNB 13 cannot identify the UEthat has transmitted the preamble at the time of detection of the PRACHpreamble. This is because the PRACH preamble does not include anyidentifier of the UE that has transmitted the preamble.

In Step S106, the MTC UE 11 transmits a message for requestingestablishment of a radio connection (RRC connection) in response toreceiving the random access response (RRC Connection Request). In StepS106, the MTC UE 11 may inform the eNB 13 that the access is a delaytolerant access. Further, the MTC UE 11 may use any one of ECM-specificradio resources or any one of ECM-specific transmission modes (e.g.,repeated transmission of a PUSCH) to transmit the RRC Connection Requestmessage.

In Step S107, the eNB 13 transmits configuration information necessaryto establish the radio connection (RRC connection) in response toreceiving the RRC Connection Request from the MTC UE 11 (RRC ConnectionSetup). In Step S108, the MTC UE 11 transmits a completion messageindicating completion of the establishment of the radio connection (RRCconnection) (RRC Connection Setup Complete). In Steps S107 and S108, anyone of ECM-specific radio resources or any one of ECM-specifictransmission modes may be used.

In Step S109, the eNB 13 transmits radio resource configurationinformation (Radio Resource Configuration) to the MTC UE 11. Thetransmission in Step S108 is performed in a procedure for establishingan EPS bearer based on a NAS message (e.g., NAS: Service Request, NAS:Attach Request) from the MTC UE 11 (not shown). The radio resourceconfiguration information in Step S108 may contain ECM configurationinformation (ECM configuration) necessary to execute the ECM. The ECMconfiguration information (ECM configuration) includes, for example,configuration information regarding coverage enhancement processing(e.g., PDSCH/PUSCH repetition) applied to transmission of user data orcontrol data (e.g., Hybrid Automatic Repeat Request (HARQ) ACK/NACK, andChannel State Information (CSI)) after establishment of the EPS bearer.

In Step S110, the MTC UE 11 performs data communication using thecoverage enhancement processing in the ECM in accordance with the radioresource configuration information and the ECM configuration information(M2M data with ECM).

FIG. 3 is a sequence diagram showing another example of the operationsof the MTC UE 11 and the eNB 13 according to this embodiment. FIG. 3shows only the messages that are necessary for explanation of thisembodiment and some messages included in the procedure specified in theLTE standard are not shown.

The processes in Steps S201 to S203 in FIG. 3 are similar to those inSteps S101 to S103 in FIG. 2. In Step S204, the MTC UE 11 transmits arandom access preamble (PRACH Preamble). In the example shown in FIG. 3,the MTC UE 11 cannot use the ECM-specific radio resources to transmitthe PRACH preamble. Accordingly, the MTC UE 11 transmits the PRACHpreamble using any one of resources commonly used by the normal UE 12.In Step S205, the eNB 13 transmits a random access response in responseto detection of the PRACH preamble (Random Access Response).

In Step S206, the MTC UE 11 transmits a message for requestingestablishing a radio connection (RRC connection) in response toreceiving the random access response (RRC Connection Request). In StepS206, the MTC UE 11 may inform the eNB 13 that the access is a delaytolerant access. Further, the MTC UE 11 may transmit the secondnotification (ECM activated) indicating that the ECM is being executedusing the RRC Connection Request message in Step S206. In order totransmit the second notification, an information element (IE) named, forexample, “ECM status” (or ECM process, ECM flag) may be defined. Forexample, when the ECM status is set to a true value or a value“Activated” it indicates that the MTC UE 11 is executing the ECM. On theother hand, when the ECM status is set to a false value or a value“Not-activated”, it may indicate that the ECM is not being executed.Further, the second notification may be one-bit flag, which indicatesthat the ECM is being executed when the value of the flag is 1 andindicates that the ECM is not being executed when the value of the flagis 0.

During Steps S201 to S206, the MTC UE 11 may receive predetermineddownlink messages (e.g., paging, broadcast information (PBCH or SIB))using any one of the ECM-specific processing.

In Step S207, the eNB 13 transmits configuration information necessaryto establish the radio connection (RRC connection) in response toreceiving the RRC Connection Request from the MTC UE 11 (RRC ConnectionSetup). In Step S208, the MTC UE 11 transmits a completion messageindicating completion of the establishment of the radio connection (RRCconnection) (RRC Connection Setup Complete). The second notification(ECM activated) may be transmitted using the RRC Connection SetupComplete message in Step S208 in place of the RRC Connection Requestmessage in Step S206.

The processes in Steps S209 and S210 are similar to those in Steps S109and S110 in FIG. 2.

Second Embodiment

A configuration example of a radio communication system according tothis embodiment may be the same as that of FIG. 1 described in the firstembodiment. In this embodiment, a modified example of the specificsequences described in the first embodiment is described. In thespecific examples shown in FIGS. 2 and 3, the MTC UE 11 determines theexecution of the ECM and the eNB 13 complies with the determination bythe MTC UE 11. However, in some cases, the determination by the MTC UE11 may be incorrect. An eNB 23 according to this embodiment does notcompletely comply with the determination by an MTC UE 21 andadditionally determines whether the ECM requested by the MTC UE 21 istruly necessary.

FIG. 4 is a sequence diagram showing one example of operations of theMTC UE 21 and the eNB 23 according to this embodiment. FIG. 4 shows onlythe messages that are necessary for explanation of this embodiment andsome messages included in the procedure specified in the LTE standardare not shown.

The process in Step S301 of FIG. 4 is similar to that in Step S101 inFIG. 2. In Step S302, the MTC UE 21 determines whether the ECM isrequired (ECM decision). FIG. 4 shows a case in which the MTC UE 21requires the ECM. Accordingly, in Step S303, the MTC UE 21 transmits amessage for requesting establishment of a radio connection (RRCconnection) (RRC Connection Request). In FIG. 4, the first and secondsteps of the random access procedure (i.e., transmission of a PRACHpreamble and reply of a Random Access Response) are not shown.

In Step S303, the MTC UE 21 may inform the eNB 23 that the access is adelay tolerant access. Further, the MTC UE 21 may transmit the secondnotification (ECM Request) indicating that the MTC UE 21 requires theECM using the RRC Connection Request message in Step S303. This secondnotification (ECM Request) requests the eNB 23 to execute the ECM forthe MTC UE 21 (the coverage enhancement processing in the ECM).

In Step S304, the eNB 23 transmits configuration information necessaryto establish a radio connection (RRC connection) in response toreceiving the RRC Connection Request from the MTC UE 21 (RRC ConnectionSetup). In Step S305, the MTC UE 21 transmits a completion messageindicating completion of the establishment of the radio connection (RRCconnection) (RRC Connection Setup Complete). The second notification(ECM Request) may be transmitted using the RRC Connection Setup Completemessage in Step S305 in place of the RRC Connection Request message inStep S303.

In Step S306, the eNB 23 determines whether the ECM is necessary for theMTC UE 21 (or whether to execute the ECM for the MTC UE 21) (ECMdecision). In the determination in Step S306, the eNB 23 may useparameters similar to those used in the determination of necessity ofthe ECM by the MTC UE 11 described in the first embodiment.

FIG. 4 shows a case in which the eNB 23 determines that the ECM isnecessary (or the ECM should be executed) for the MTC UE 21.Accordingly, in Step S307, the eNB 23 transmits radio resourceconfiguration information (Radio Resource Configuration) to the MTC UE21 (RRC Connection Reconfiguration). The transmission in Step S307 maybe performed in a procedure for establishing an EPS bearer based on aNAS message (e.g., NAS: Service Request, NAS: Attach Request) from theMTC UE 21 (not shown). The radio resource configuration information inStep S307 may contain ECM configuration information (ECM configuration)necessary to execute the ECM. Further, the radio resource configurationinformation in Step S307 may contain information for explicitlyinstructing the MTC UE 21 to execute the ECM.

In Step S308, the MTC UE 21 starts executing the ECM in response to theexplicit or implicit instruction from the eNB 23 in Step S307 (ECMstart). In Step S309, the MTC UE 21 performs data communication usingthe coverage enhancement processing in the ECM in accordance with theradio resource configuration information and the ECM configurationinformation (M2M data with ECM).

Third Embodiment

A configuration example of a radio communication system according tothis embodiment may be the same as that of FIG. 1 described in the firstembodiment. In this embodiment, a modified example of the specificsequences described in the first and second embodiments (FIGS. 2, 3, and4) is described.

It can be said that the procedure described in this embodiment is acombination of the procedures shown in FIG. 2 (or FIG. 3) and FIG. 4.That is, in this embodiment, an MTC UE 31 itself determines necessity ofthe ECM, starts executing the ECM based on this determination, andinforms an eNB 33 that the MTC UE 31 requires the ECM (or is executingthe ECM) (second notification). The eNB 33 determines whether the ECM isnecessary for the MTC UE 31 in response to receiving the secondnotification from the MTC UE 31. When the eNB 33 determines that the ECMis necessary, the eNB 33 transmits ECM configuration information to theMTC UE 31 and when the eNB 33 determines that the ECM is not necessary,the eNB 33 sends an instruction to suspend (or stop) the ECM to the MTCUE 31. According to this procedure for controlling the ECM, the MTC UE31 can promptly start the ECM based on the determination by the MTC UE31 itself. Further, the eNB 33 can check the validity of thedetermination by the MTC UE 31 of necessity of the ECM and can reject aninappropriate determination, i.e., the eNB 33 can stop the ECM.

FIG. 5 is a sequence diagram showing one example of operations of theMTC UE 31 and the eNB 33 according to this embodiment. FIG. 5 shows onlythe messages that are necessary for explanation of this embodiment andsome messages included in the procedure specified in the LTE standardare not shown.

The processes in Steps S401 to S403 in FIG. 5 are similar to those inSteps S101 to S103 shown in FIG. 2. In Step S404, the MTC UE 31transmits a completion message indicating completion of establishment ofa radio connection (RRC connection) (RRC Connection Setup Complete). InFIG. 5, the first to fourth steps of the random access procedure (i.e.,steps from PRACH preamble transmission by the MTC UE 31 to RRCConnection Setup message transmission by the eNB 33) are not shown.

The MTC UE 31 may transmit the second notification (ECM Request)indicating that the MTC UE 31 requires the ECM using the RRC ConnectionSetup Complete message in Step S404. This second notification (ECMRequest) requests the eNB 33 to execute the ECM (the coverageenhancement processing in the ECM) for the MTC UE 31. The secondnotification (ECM Request) may be transmitted using an RRC ConnectionRequest message (not shown) in place of the RRC Connection SetupComplete message in Step S404.

In Step S405, the eNB 33 determines whether the ECM is necessary for theMTC UE 31 (or whether to execute the ECM for the MTC UE 31) (ECMdecision). In the determination in Step S405, the eNB 33 may useparameters similar to those used in the determination of necessity ofthe ECM by the MTC UE 11 described in the first embodiment.

Steps S406 and S407 show a case in which the eNB 33 determines that theECM is necessary (or the ECM is executed) for the MTC UE 31 (case 1shown in FIG. 5). In Step S406, the eNB 33 transmits radio resourceconfiguration information (Radio Resource Configuration) to the MTC UE31 (RRC Connection Reconfiguration). The radio resource configurationinformation in Step S406 may contain ECM configuration information (ECMconfiguration) necessary to execute the ECM. Further, the radio resourceconfiguration information in Step S406 may contain information forexplicitly instructing the MTC UE 31 to execute the ECM. In Step S407,the MTC UE 31 performs data communication using the coverage enhancementprocessing in the ECM in accordance with the radio resourceconfiguration information and the ECM configuration information (M2Mdata with ECM).

On the other hand, Steps S408 to S410 show a case the eNB 33 determinesthat the ECM is not necessary for the MTC UE 31 (or the ECM should besuspended or stopped) (case 2 shown in FIG. 5). In Step S408, the eNB 33transmits resource configuration information (Radio ResourceConfiguration) to the MTC UE 31 (RRC Connection Reconfiguration). Theradio resource configuration information in Step S408 contains aninstruction to suspend (or stop) execution of the ECM (ECM deactivated).In Step S409, the MTC UE 31 suspends (or stops) execution of the ECM(ECM stop). In Step S410, the MTC UE 31 performs data communicationwithout using the coverage enhancement processing in the ECM (M2M datawithout ECM).

Fourth Embodiment

A configuration example of a radio communication system according tothis embodiment may be to the same as that of FIG. 1 described in thefirst embodiment. In this embodiment, a modified example of the specificsequences described in the third embodiment (FIG. 5) is described.

In this embodiment, similar to the MTC UE 31 according to the thirdembodiment, an MTC UE 41 itself determines necessity of the ECM, startsexecuting the ECM based on this determination, and informs the eNB 43that the MTC UE 41 requires the ECM (or is executing the ECM) (secondnotification). After that, the MTC UE 41 suspends (or stops) executionof the ECM to wait for a determination by the eNB 43. With regard tothis point, this embodiment is different from the third embodiment. Forexample, the MTC UE 41 may starts the coverage enhancement processing inthe ECM (e.g., reception of a repeated PBCH, repeated transmission of aPRACH preamble, and repetition of a PDSCH/PUSCH) when accessing to theeNB 43 and continue the processing until the radio connection (RRCconnection) has been established, and then suspend the execution of theECM. In other words, the MTC UE 41 may execute the ECM during at leastthe random access procedure (RACH procedure) and the RRC connectionestablishment procedure and then suspend execution of the ECM.

Similar to the eNB 33 according to the third embodiment, the eNB 43according to this embodiment determines whether the ECM is necessary forthe MTC UE 41 in response to receiving the second notification from theMTC UE 41. Upon determining that the ECM is necessary, the eNB 43transmits ECM configuration information to the MTC UE 41 and upondetermining that the ECM is not necessary, transmits an instruction tosuspend (or stop) the ECM to the MTC UE 41. The MTC UE 41 re-starts theECM that has been suspended (stopped) in response to receiving the ECMconfiguration information from the eNB 43.

According to the procedure for controlling the ECM as stated above,similar to the third embodiment, the MTC UE 41 can promptly start theECM based on the determination by the MTC UE 41 itself. In particular,by temporarily executing the ECM until at least the radio connection(RRC connection) has been established, it is possible to avoid failureof the first access by the MTC UE 41 to the eNB 43 (e.g., random accessusing a PRACH or RRC Connection establishment). On the other hand, theeNB 43 can check the validity of the determination by the MTC UE 31 ofnecessity of the ECM and selectively start the ECM only when it isappropriate.

FIG. 6 is a sequence diagram showing one example of operations of theMTC UE 41 and the eNB 43 according to this embodiment. FIG. 6 shows onlythe messages that are necessary for explanation of this embodiment andsome messages included in the procedure specified in the LTE standardare not shown.

The processes in Steps S501 to S504 in FIG. 6 are similar to those inSteps S401 to S404 in FIG. 5. In Step S505, the MTC UE 41 suspends orstops execution of the ECM (i.e., the coverage enhancement processing inthe ECM) after Step S504, that is, after establishment of the RRCconnection (ECM Stop).

The process in Step S506 is similar to that in Step S405 of FIG. 5. Thatis, the eNB 43 determines whether the ECM is necessary for the MTC UE 41(or whether to execute the ECM for the MTC UE 41) (ECM decision).

Steps S507 to S509 show a case in which the eNB 43 determines that theECM is necessary (or the ECM is executed) for the MTC UE 41 (case 1shown in FIG. 6). The process in Step S507 is similar to that in StepS406 in FIG. 5. That is, the eNB 43 transmits radio resourceconfiguration information (Radio Resource Configuration) to the MTC UE41 (RRC Connection Reconfiguration). In Step S508, the MTC UE 41 startsor re-starts execution of the ECM in response to the instruction fromthe eNB 43 (ECM start). Then in Step S509, the MTC UE 41 performs datacommunication using the coverage enhancement processing in the ECM inaccordance with the radio resource configuration information and the ECMconfiguration information (M2M data with ECM).

On the other hand, Steps S510 and S511 show a case the eNB 43 determinesthat the ECM is not necessary for the MTC UE 41 (case 2 shown in FIG.6). In Step S510, the eNB 43 transmits radio resource configurationinformation (Radio Resource Configuration) to the MTC UE 41 (RRCConnection Reconfiguration). The radio resource configurationinformation in Step S510 may explicitly indicate that the ECM is notexecuted. In Step S511, the MTC UE 41 performs data communicationwithout using the coverage enhancement processing in the ECM (M2M datawithout ECM).

Lastly, configuration examples of the MTC UEs and the eNBs according tothe above embodiments are described below. Each of the MTC UEs 11, 21,31, and 41 described in the first to fourth embodiments may include atransceiver to communicate with an eNB and a controller that is coupledto the transceiver. The controller executes the communication controlregarding the ECM performed by the MTC UE 11, 21, 31, or 41 described inthe first to fourth embodiments.

Each of the eNBs 13, 23, 33, and 43 described in the first to fourthembodiments may include a transceiver to communicate with UEs includingMTC UEs and a controller that is coupled to the transceiver. Thecontroller executes the communication control regarding the ECMperformed by the eNB 13, 23, 33, or 43 described in the first to fourthembodiments.

FIGS. 7 and 8 are block diagrams showing configuration examples of theMTC UE 11 and the eNB 13 according to the first embodiment,respectively. With reference to FIG. 7, the MTC UE 11 includes atransceiver 111 and a controller 112. The transceiver 111 is configuredto communicate with the eNB 13. The controller 112 is configured tocontrol execution of the coverage enhancement processing regarding theECM in the MTC UE 11 in accordance with instructions from the eNB 13.Specifically, the controller 112 is configured to receive the firstnotification from the eNB 13 via the transceiver 111. Further, thecontroller 112 is configured to transmit the second notification to theeNB 13 via the transceiver 111 when establishing a radio connection (RRCconnection) with the eNB 13 after reception of the first notification orwhile performing a procedure for establishing an EPS bearer afterreception of the first notification.

With reference to FIG. 8, the eNB 13 includes a transceiver 131 and acontroller 132. The transceiver 131 is configured to communicate withUEs including the MTC UEs 11 and the normal UE 12. The controller 132 isconfigured to control communication between the MTC UEs 11 and the eNB13 using the coverage enhancement processing regarding the ECM.Specifically, the controller 132 is configured to transmit the firstnotification indicating that the specific coverage enhancementprocessing for the MTC UEs 11 (that is, the coverage enhancementprocessing in the ECM) is supported in the cell 130 of the eNB 13 viathe transceiver 131.

The controllers included in the MTC UEs and the eNBs according to theabove embodiments may be implemented by causing a computer including atleast one processor (e.g., microprocessor, Micro Processing Unit (MPU),Central Processing Unit (CPU)) to execute a program. Specifically, oneor more programs containing set of instructions that causes a computerto perform algorithms regarding the MTC UE or the eNB described usingthe sequence diagrams and the like may be supplied to the computer.

These programs can be stored and provided to a computer using any typeof non-transitory computer readable media. Non-transitory computerreadable media include any type of tangible storage media. Examples ofnon-transitory computer readable media include magnetic storage media(such as flexible disks, magnetic tapes, hard disk drives, etc.),optical magnetic storage media (e.g., magneto-optical disks), CompactDisc Read Only Memory (CD-ROM), CD-R, CD-R/W, and semiconductor memories(such as mask ROM, Programmable ROM (PROM), Erasable PROM (EPROM), flashROM, Random Access Memory (RAM), etc.). These programs may be providedto a computer using any type of transitory computer readable media.Examples of transitory computer readable media include electric signals,optical signals, and electromagnetic waves. Transitory computer readablemedia can provide the program to a computer via a wired communicationline (e.g., electric wires, and optical fibers) or a wirelesscommunication line.

Other Embodiments

The explanations of the aforementioned embodiments have been providedwith regard to the situation in which MTC UEs are configured with thespecial operation mode, i.e., the Enhanced Coverage Mode (ECM) andperform the coverage enhancement processing (e.g., RACH repetition andPDSCH/PUSCH repetition) regarding the ECM. However, the MTC UEs is onlyrequired to execute the special coverage enhancement processing (e.g.,RACH repetition and PDSCH/PUSCH repetition) and do not have to beconfigured with the special operation mode (i.e., ECM). In other words,the MTC UEs 11, 21, 31, and 41 may execute the special coverageenhancement processing (e.g., RACH repetition and PDSCH/PUSCHrepetition) in accordance with the radio resource configuration withoutsetting the special operation mode such as the ECM or without receivingan instruction regarding the special operation mode.

The explanations of the above embodiments have been provided with regardto the ECM, however the technical ideas described in these embodimentsmay be applied to a case in which a radio network (e.g., eNB) causes M2Mterminals (MTC UEs) to execute special processing other than the ECM.

Further, the terms “normal terminals (UE)” and “M2M terminals (MTC UEs)”used in the above explanation are also referred to as “user terminals”and “non-user terminals”, respectively.

Further, in the above embodiments, the LTE system has been mainlydescribed. However, these embodiments may be applied to radiocommunication systems other than the LTE system (e.g., 3GPP UMTS, 3GPP2CDMA2000 system (1×RTT, HRPD), GSM/GPRS system, or WiMAX system).

When the aforementioned embodiments are applied to 3GPP UMTS, theoperations of the eNB (eNB 13, 23, 33, or 43) according to theembodiments may be performed by a NodeB, an RNC or the combinationthereof. In other words, the term “base station” used in thespecification and claims means one or more entities installed in a radioaccess network, for example, any one or combination of a NodeB and anRNC in the UMTS.

Further, the above embodiments are merely examples of applications ofthe technical ideas obtained by the present inventor. Needless to say,these technical ideas are not limited to the above embodiments and theabove embodiments may be modified in various ways.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2014-015866, filed on Jan. 30, 2014, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   11, 21, 31, 41 M2M TERMINAL (MTC UE)-   13, 23, 33, 43 BASE STATION (eNB)-   14 CORE NETWORK (EPC)-   130 CELL-   111 TRANSCEIVER-   112 CONTROLLER-   131 TRANSCEIVER-   132 CONTROLLER

1-35. (canceled)
 36. A coverage enhancement capable user equipmentcomprising: a radio transceiver configured to communicate with a basestation; and a controller, wherein the controller configured to:receive, in a Physical Broadcast Channel (PBCH) from the base station, amaster information block message that includes information associatedwith a repetition number of a Physical Downlink Shared Channel (PDSCH)carrying a system information block type 1 message for the coverageenhancement; receive, in the PDSCH from the base station, one or moresystem information block messages that include the system informationblock type 1 message for the coverage enhancement; and transmit, to thebase station, a random access preamble with repetition by using one ormore specific radio resources for the coverage enhancement.
 37. Thecoverage enhancement capable user equipment according to claim 36,wherein the master information block message and the one or more systeminformation block messages are received on a broadcast channel that canbe received by user equipments not having a radio connection with thebase station and not being reachable by paging since locations of theuser equipments are not registered in the core network.
 38. The coverageenhancement capable user equipment according to claim 37, wherein thebroadcast channel comprises a Broadcast Control Channel (BCCH) in LongTerm Evolution (LTE).
 39. The coverage enhancement capable userequipment according to claim 36, wherein the one or more systeminformation block messages comprise configuration information for acoverage enhancement processing and imply that the coverage enhancementprocessing is supported by the base station.
 40. The coverageenhancement capable user equipment according to claim 36, wherein thecontroller is further configured to transmit a request message forrequesting establishment of a radio connection or a completion messageindicating completion of establishment of a radio connection.
 41. Thecoverage enhancement capable user equipment according to claim 40,wherein the request message comprises a Radio Resource Control (RRC)Connection Request message in Long Term Evolution (LTE), and thecompletion message comprises an RRC Connection Setup Complete message inLTE.
 42. The coverage enhancement capable user equipment according toclaim 36, wherein the controller is further configured to transmit aRadio Resource Control (RRC) message together with a Non-access stratum(NAS) message for requesting establishment of a bearer.
 43. The coverageenhancement capable user equipment according to claim 36, wherein thecontroller is configured to decide to execute a coverage enhancementprocessing in the coverage enhancement capable user equipment andcontrols communication using the coverage enhancement processing betweenthe coverage enhancement capable user equipment and the base station.44. The coverage enhancement capable user equipment according to claim43, wherein the controller is configured to continue executing thecoverage enhancement processing until having received from the basestation an instruction that explicitly or implicitly indicates stop ofthe coverage enhancement processing.
 45. The coverage enhancementcapable user equipment according to claim 43, wherein the controller isconfigured to continue executing the coverage enhancement processinguntil completion of data communication with the coverage enhancementcapable user equipment.
 46. The coverage enhancement capable userequipment according to claim 43, wherein the controller is configured tocontinue executing the coverage enhancement processing during a delaytolerant access.
 47. The coverage enhancement capable user equipmentaccording to claim 43, wherein the controller is configured to continueexecuting the coverage enhancement processing until completion ofestablishment of a radio connection.
 48. The coverage enhancementcapable user equipment according to claim 43, wherein the controller isconfigured to continue executing the coverage enhancement processinguntil completion of establishment of a bearer.
 49. The coverageenhancement capable user equipment according to claim 36, wherein, thecontroller is configured to, if the controller is instructed by the basestation to execute a coverage enhancement processing, continue executingthe coverage enhancement processing even after releasing a radioconnection with the base station.
 50. The coverage enhancement capableuser equipment according to claim 36, wherein, the controller isconfigured to, if the controller is instructed by the base station toexecute a coverage enhancement processing, continue executing thecoverage enhancement processing even while repeating establishment andrelease of a radio connection with the base station.
 51. The coverageenhancement capable user equipment according to claim 36, wherein, thecontroller is configured to, if controller is instructed by the basestation to execute a coverage enhancement processing, continue executingthe coverage enhancement processing during a delay tolerant access. 52.A base station comprising: a radio transceiver configured to communicatewith a coverage enhancement capable user equipment; and a controllerconfigured to: transmit, in a Physical Broadcast Channel (PBCH) to thecoverage enhancement capable user equipment via the radio transceiver, amaster information block message that includes information associatedwith a repetition number of a Physical Downlink Shared Channel (PDSCH)carrying a system information block type 1 message for the coverageenhancement; transmit, in the PDSCH to the coverage enhancement capableuser equipment via the radio transceiver, one or more system informationblock messages that include the system information block type 1 messagefor the coverage enhancement; and receive, from the coverage enhancementcapable user equipment via the radio transceiver, a random accesspreamble with repetition by using one or more specific radio resourcesfor the coverage enhancement.
 53. The base station according to claim52, wherein the master information block message and the one or moresystem information block messages are transmitted on a broadcast channelthat can be received by user equipments not having a radio connectionwith the base station and not being reachable by paging since locationsof the user equipments are not registered in the core network.
 54. Thebase station according to claim 53, wherein the broadcast channelcomprises a Broadcast Control Channel (BCCH) in Long Term Evolution(LTE).
 55. The base station according to claim 52, wherein the one ormore system information block messages comprise configurationinformation for a coverage enhancement processing and imply that thecoverage enhancement processing is supported by the base station. 56.The base station according to claim 52, wherein the controller isfurther configured to receive a request message for requestingestablishment of a radio connection or a completion message indicatingcompletion of establishment of a radio connection.
 57. The base stationaccording to claim 56, wherein the request message comprises a RadioResource Control (RRC) Connection Request message in Long Term Evolution(LTE), and the completion message comprises an RRC Connection SetupComplete message in LTE.
 58. The base station according to claim 52,wherein the controller is further configured to receive a Radio ResourceControl (RRC) message together with a Non-access stratum (NAS) messagefor requesting establishment of a bearer.
 59. The base station accordingto claim 52, wherein the controller is configured to decide to execute acoverage enhancement processing for the Coverage enhancement capableuser equipment in response to receiving the random access preamble andcontrols communication using the coverage enhancement processing betweenthe Coverage enhancement capable user equipment and the base station.60. A method performed by a coverage enhancement capable user equipment,the method comprising: receiving, in a Physical Broadcast Channel (PBCH)from a base station, a master information block message that includesinformation associated with a repetition number of a Physical DownlinkShared Channel (PDSCH) carrying a system information block type 1message for the coverage enhancement; receiving, in the PDSCH from thebase station, one or more system information block messages that includethe system information block type 1 message for the coverageenhancement; and transmitting, to the base station, a random accesspreamble with repetition by using one or more specific radio resourcesfor the coverage enhancement.
 61. A method performed by a base station,the method comprising: transmitting in a Physical Broadcast Channel(PBCH) to a coverage enhancement capable user equipment, a masterinformation block message that includes information associated with arepetition number of a Physical Downlink Shared Channel (PDSCH) carryinga system information block type 1 message for the coverage enhancement;transmitting, in the PDSCH to the coverage enhancement capable userequipment via the radio transceiver, one or more system informationblock messages that include the system information block type 1 messagefor the coverage enhancement; and receiving, from the coverageenhancement capable user equipment via the radio transceiver, a randomaccess preamble with repetition by using one or more specific radioresources for the coverage enhancement.
 62. A non-transitory computerreadable medium storing a program for causing a computer to perform amethod regarding a coverage enhancement capable user equipment, whereinthe method comprises: receiving, in a Physical Broadcast Channel (PBCH)from a base station, a master information block message that includesinformation associated with a repetition number of a Physical DownlinkShared Channel (PDSCH) carrying a system information block type 1message for the coverage enhancement; receiving, in the PDSCH from thebase station, one or more system information block messages that includethe system information block type 1 message for the coverageenhancement; and transmitting, to the base station, a random accesspreamble with repetition by using one or more specific radio resourcesfor the coverage enhancement.
 63. A non-transitory computer readablemedium storing a program for causing a computer to perform a methodregarding a base station, wherein the method comprises: transmitting ina Physical Broadcast Channel (PBCH) to a coverage enhancement capableuser equipment, a master information block message that includesinformation associated with a repetition number of a Physical DownlinkShared Channel (PDSCH) carrying a system information block type 1message for the coverage enhancement; transmitting, in the PDSCH to thecoverage enhancement capable user equipment via the radio transceiver,one or more system information block messages that include the systeminformation block type 1 message for the coverage enhancement; andreceiving, from the coverage enhancement capable user equipment via theradio transceiver, a random access preamble with repetition by using oneor more specific radio resources for the coverage enhancement.